1. Field of the Invention
The present invention relates generally to an information storage device, and more particularly to a magneto-optical disk drive having a mechanism for detecting a misalignment between an optical head and a magnetic head.
2. Description of the Related Art
Increasing a recording density in a magneto-optical disk drive has been progressively required and various systems for information recording have been developed. According to an optical modulation recording system adopted by the ISO standard, a laser beam is modulated with recording data while an external magnetic field is being applied in a fixed direction, thereby recording information on a magneto-optical recording medium. In this optical modulation recording system, an information recording density is limited by the size of a beam spot on the magneto-optical recording medium.
In contrast therewith, according to a magnetic field modulation recording system, an external magnetic field is modulated with recording data while a laser beam having a fixed intensity is being directed onto a magneto-optical recording medium. In this magnetic field modulation recording system, beam spots can be overlapped on the magneto-optical recording medium, so that this system is considered to be more advantageous for high-density recording than the optical modulation recording system. Since the external magnetic field is modulated with the recording data at a high speed in the magnetic field modulation recording system, a flying magnetic head is used as a magnetic head in this system. The flying magnetic head used in this system is substantially the same in shape and operation principle as that used in a magnetic disk drive. When a magneto-optical disk (as the magneto-optical recording medium) is rotated, the magnetic head flies from the surface of the disk at a height of about 10 xcexcm to record data in a beam spot.
The flying magnetic head has a magnetization range that is narrower than that of an electromagnetic bias field used in a conventional optical modulation recording system. Further, it is expected that the beam spot size formed by an optical head and the magnetization range of the magnetic head will be reduced more in response to future higher-density recording. To attain high-density recording, the optical head and the magnetic head must be precisely aligned with each other. In a conventional magnetic field modulation recording type of magneto-optical disk drive, the optical head and the magnetic head are aligned once in assembling the disk drive, and the disk drive is not provided with a mechanism for automatically adjusting the relative positions of the optical head and the magnetic head to correct a misalignment between the optical head and the magnetic head due to thermal deformation after assembling the disk drive.
Japanese Patent Laid-open No. Hei 5-6593 discloses a magneto-optical disk drive having such a mechanism for correcting a misalignment between the optical head and the magnetic head. In the magneto-optical disk drive disclosed in this publication, the magnetic head is moved completely independently of the optical head. Accordingly, the magnetic head requires the same operational distance as that of the optical head, causing a possibility of enlargement of an actuator. Further, misalignment detecting means is located at the rear ends of the magnetic head and the optical head, that is, on the same side as a fixed optical system having a semiconductor laser. Accordingly, a degree of freedom of design of the fixed optical system is reduced by the location of this detecting means. This disadvantage also makes it difficult to reduce the size of the disk drive.
Thus, there has not been proposed a magnetic field modulation type of magneto-optical disk drive having a misalignment correcting mechanism for automatically detecting a misalignment between the magnetic head and the optical head without enlarging the size of the disk drive. It is accordingly greatly important to provide a misalignment correcting mechanism for automatically detecting a misalignment between the magnetic head and the optical head with a simple structure in response to future higher-density recording.
In addition, the magnetic head is kept flying over the magneto-optical disk surface at a microscopic height during operation of the disk drive, so that there is always the possibility that the magnetic head may collide with the disk to cause head crash. No prior art disk drive of this kind especially has a mechanism for preventing or reducing the possibility of head crash of the magnetic head. Accordingly, it is also greatly important to provide a mechanism for preventing a collision of the magnetic head with the disk during operation of the disk drive.
It is therefore an object of the present invention to provide an information storage device having a mechanism for automatically detecting a misalignment between a magnetic head and an optical head and correcting the misalignment.
It is another object of the present invention to provide an information storage device having a mechanism for preventing a collision of a magnetic head with a disk during operation of the device to improve the reliability.
In accordance with an aspect of the present invention, there is provided an information storage device comprising a carriage; an optical head mounted on said carriage, said optical head having an objective lens and an actuator for moving said objective lens; first driving means for moving said carriage in a first direction; a magnetic head assembly mounted on said carriage and having a magnetic head; a light emitting element mounted on said optical head; and a photodetector mounted on said magnetic head assembly for detecting light emitted from said light emitting element; a misalignment between said optical head and said magnetic head being detected by using said photodetector and said light emitted from said light emitting element.
In general, a magneto-optical disk as an information recording medium has an inner-circumferential transparent portion where a transparent substrate is exposed with no magnetic coating applied. Accordingly, the misalignment between the optical head and the magnetic head is detected when the light emitting element and the photodetector are located at a position corresponding to the inner-circumferential transparent portion of the magneto-optical disk loaded into the information storage device. The information storage device further comprises second driving means for moving the magnetic head to correct the misalignment between the optical head and the magnetic head. Preferably, the second driving means is provided by a voice coil motor consisting of a coil and a permanent magnet. In one preferred embodiment, the magnetic head assembly includes a head arm and a suspension elastically supported to the head arm, and the magnetic head is mounted on the suspension.
In another preferred embodiment, the magnetic head assembly includes a head arm and a suspension rotatably supported to the head arm. Preferably, in this case, the information storage device further comprises a mechanism for lifting the magnetic head from the disk when the suspension is rotated a given angle or more relative to the head arm. This lifting mechanism keeps lifting the magnetic head from the disk during standby and during reading data recorded on the disk, whereas allowing the magnetic head to move over the disk surface at a given flying height only during writing data onto the disk.
In accordance with another aspect of the present invention, there is provided an information storage device comprising a carriage; a laser light source for emitting a laser beam; an optical head mounted on said carriage, said optical head having an objective lens, a first beam raising mirror for reflecting a first part of said laser beam toward said objective lens and transmitting a second part of said laser beam, an actuator for moving said objective lens, and a second beam raising mirror for totally reflecting said second part of said laser beam transmitted through said first beam raising mirror; first driving means for moving said carriage in a first direction; a magnetic head assembly mounted on said carriage and having a magnetic head; and a photodetector mounted on said magnetic head assembly for detecting said second part of said laser beam reflected by said second beam raising mirror; a misalignment between said optical head and said magnetic head being detected by using said photodetector and said second part of said laser beam reflected by said second beam raising mirror.
In accordance with a further aspect of the present invention, there is provided an information storage device comprising a carriage; a laser light source for emitting a laser beam; an optical head mounted on said carriage, said optical head having an objective lens, a beam raising mirror for totally reflecting said laser beam toward said objective lens, and an actuator for moving said objective lens; first driving means for moving said carriage in a first direction; a magnetic head assembly mounted on said carriage and having a magnetic head; and a photodetector mounted on said magnetic head assembly at a position adjacent to said magnetic head for detecting said laser beam reflected by said beam raising mirror and transmitted through said objective lens; a misalignment between said optical head and said magnetic head being detected by using said photodetector and said laser beam transmitted through said objective lens.